The application generally relates to a system and method for starting a compressor. The application relates more specifically to starting algorithms for a compressor that prevent hydraulic slugging and provide for proper lubrication of the compressor during the starting process.
Certain types of hermetic compressors may include an oil sump in the bottom of the compressor housing to store oil that is used to lubricate the components of the compressor. During operation of the compressor, oil is pumped from the oil sump into the components of the compressor to provide lubrication to the compressor components. In addition, the compressor housing can be filled with refrigerant vapor associated with the compression process. However, once the compressor is no longer operating or is shutdown, the refrigerant vapor in the compressor housing and other system elements can migrate and/or condense into the oil sump to form a mixture of liquid refrigerant and oil.
Starting the compressor at full speed and torque with liquid refrigerant in the oil sump, can result in damage to the compressor components. The damage can occur from inadequate lubrication due to oil dilution by the liquid refrigerant or as a result of the attempted compression of the liquid refrigerant and oil mixture (hydraulic slugging). One technique to remove or prevent liquid refrigerant from migrating and/or condensing in the oil sump is to use a heater to maintain the temperature of the oil sump and evaporate any liquid refrigerant that may be present. However, there are several drawbacks to this technique in that the continuous operation of the heater can have substantial power requirements that reduce system efficiency and the manufacturing costs associated with the heater and/or its control can thereby increase the system and operating costs.
Therefore what is needed is a system and method for starting a compressor that can minimize the effect of liquid refrigerant in the lubricating oil supply for the compressor.